chore: add premlinenary CDC interfaces

Author: Martin Fischer

micropython/usbd/cdc.py

@@ -0,0 +1,86 @@
+# MicroPython USB CDC module
+# MIT license; Copyright (c) 2022 Martin Fischer
+from .device import (
+    USBInterface,
+    get_usbdevice
+)
+from .utils import (
+    endpoint_descriptor,
+    EP_OUT_FLAG
+)
+from micropython import const
+import ustruct
+
+_DEV_CLASS_MISC = const(0xef)
+_CS_DESC_TYPE = const(0x24)   # CS Interface type communication descriptor
+_ITF_ASSOCIATION_DESC_TYPE = const(0xb)  # Interface Association descriptor
+
+# CDC control interface definitions
+_CDC_ITF_CONTROL_CLASS = const(2)
+_CDC_ITF_CONTROL_SUBCLASS = const(2)  # Abstract Control Mode
+_CDC_ITF_CONTROL_PROT = const(0)   # no protocol
+
+# CDC data interface definitions
+_CDC_ITF_DATA_CLASS = const(0xa)
+_CDC_ITF_DATA_SUBCLASS = const(0)
+_CDC_ITF_DATA_PROT = const(0)   # no protocol
+
+
+def setup_CDC_device():
+    # CDC is a composite device, consisting of multiple interfaces
+    # (CDC control and CDC data)
+    # therefore we have to make sure that the association descriptor
+    # is set and that it associates both interfaces to the logical cdc class
+    usb_device = get_usbdevice()
+    usb_device.device_class = _DEV_CLASS_MISC
+    usb_device.device_subclass = 2
+    usb_device.device_protocol = 1   # Itf association descriptor
+
+
+class CDCControlInterface(USBInterface):
+    # Implements the CDC Control Interface
+
+    def __init__(self, interface_str):
+        super().__init__(_CDC_ITF_CONTROL_CLASS, _CDC_ITF_CONTROL_SUBCLASS,
+                         _CDC_ITF_CONTROL_PROT)
+
+    def get_itf_descriptor(self, num_eps, itf_idx, str_idx):
+        # CDC needs a Interface Association Descriptor (IAD)
+        # first interface is zero, two interfaces in total
+        desc = ustruct.pack("<BBBBBBBB", 8, _ITF_ASSOCIATION_DESC_TYPE, itf_idx, 2,
+                            _CDC_ITF_CONTROL_CLASS, _CDC_ITF_CONTROL_SUBCLASS,
+                            _CDC_ITF_CONTROL_PROT, 0)  # "IAD"
+
+        itf, strs = super().get_itf_descriptor(num_eps, itf_idx, str_idx)
+        desc += itf
+        # Append the CDC class-specific interface descriptor
+        # see also USB spec document CDC120-track, p20
+        desc += ustruct.pack("<BBBH", 5, _CS_DESC_TYPE, 0, 0x0120)  # "Header"
+        desc += ustruct.pack("<BBBBB", 5, _CS_DESC_TYPE, 1, 0, 1)   # "Call Management"
+        desc += ustruct.pack("<BBBB", 4, _CS_DESC_TYPE, 2, 2)  # "Abstract Control"
+        desc += ustruct.pack("<BBBH", 5, _CS_DESC_TYPE, 6, itf_idx, 1)  # "Union"
+        return desc, strs
+
+    def get_endpoint_descriptors(self, ep_addr, str_idx):
+        self.ep_in = endpoint_descriptor((ep_addr + 1) | EP_OUT_FLAG, "interrupt", 8, 16)
+        return (self.ep_in, [], ((ep_addr+1) | EP_OUT_FLAG,))
+
+
+class CDCDataInterface(USBInterface):
+    # Implements the CDC Data Interface
+
+    def __init__(self, interface_str):
+        super().__init__(_CDC_ITF_DATA_CLASS, _CDC_ITF_DATA_SUBCLASS,
+                         _CDC_ITF_DATA_PROT)
+
+    def get_endpoint_descriptors(self, ep_addr, str_idx):
+        # XXX OUT = 0x00 but is defined as 0x80?
+        self.ep_in = (ep_addr + 2) | EP_OUT_FLAG
+        self.ep_out = (ep_addr + 2) & ~EP_OUT_FLAG
+        print("cdc in={} out={}".format(self.ep_in, self.ep_out))
+        # one IN / OUT Endpoint
+        e_out = endpoint_descriptor(self.ep_out, "bulk", 64, 0)
+        e_in = endpoint_descriptor(self.ep_in, "bulk", 64, 0)
+        desc = e_out + e_in
+        return (desc, [], (self.ep_out, self.ep_in))
+